The present invention relates to a lens barrel drive mechanism which drives a lens barrel such as for driving a zooming mechanism.
To perform auto-focusing, zooming and other camera actions, the lens barrel in the camera has to be moved back and forth, and various types of lens barrel drive mechanism have been proposed and developed. A typical lens barrel drive mechanism comprises a motor, a drive gear secured to the output shaft of the motor and a reduction gear train for reducing the number of revolutions of the drive gear.
In order to obtain maximum accuracy in adjustment while focusing or zooming the lens using such lens barrel drive mechanism, it is important that the amount of movement of the lens barrel be controlled accurately. To meet this need, it has been proposed that the lens barrel drive mechanism of the type under consideration be equipped with a system for detecting the amount of movement of the lens barrel which includes a pulse plate provided parallel to the first gear or an intermediate gear in the reduction gear train and which rotates integrally with that gear and a photo-interrupter which is so shaped as that parts of the photo-interrupter are located on both sides of the pulse plate.
This detection system is usually installed in a limited space within the small camera body, so considerable difficulty is encountered in the mounting procedure. In particular, the pulse plate inevitably has only a limited area to put in because as already mentioned it is provided parallel to each of the gears in the reducing gear train. Therefore, in an attempt to secure a wide enough area for installing the pulse plate and other elements of the detection system, a certain part of the camera body such as the lower part is extended. However, this is unfavorable to the purpose of reducing the size of the camera body.
Further, gears with a smaller number of teeth must be used to increase the rotating speed of the pulse plate sufficiently to achieve precise detection of the amount of lens barrel movement. This adds the further increase of the required installation space and the manufacturing cost is increased accordingly.
The present invention has been accomplished under these circumstances and has as an object providing a lens barrel drive mechanism that meets the purpose of achieving compactness by not requiring any additional space to install the system of detecting the amount of lens barrel movement and which can be fabricated at minimum cost without compromising the essential need for precise detection of the amount of lens barrel movement.
According to the present invention, the detecting system is provided in a generally triangular space between a cell compartment and a film cartridge compartment in the camera body.
The detecting system is provided not in an additionally created space but in the heretofore unused dead space and this is favorable to the purpose of reducing the size of the camera body.
Further, if the detecting system is directly coupled to the output shaft of the fast rotating motor, it is possible to dispense with any accelerating mechanism such as a gear or gears with a smaller number of teeth that have been necessary in the related art. That is, the amount of lens barrel movement can be detected with high precision and it is possible to realize a compact and precise lens barrel drive mechanism with minimum increase in the manufacturing cost.
As a preferred embodiment, the present invention provides a lens barrel drive mechanism having a worm secured to an output shaft of a lens barrel drive motor and a gear train by which the rotating force of a worm wheel meshing with said worm is transmitted to the lens barrel, said drive mechanism further including a system of detecting the number of revolutions of said output shaft as associated with the amount of extension of said lens barrel, said system being provided in the generally triangular space between a cell compartment and a film cartridge compartment in the camera body.
It is more preferable that the worm is provided at the initial stage of the gear train which is directly coupled to said output shaft, and said number-of-revolutions detecting system is provided on said worm.
The number-of-revolutions detecting system may comprise a pulse plate secured to a rotating shaft which rotates integrally with the worm, and a photo-interrupter which detects the rotation of said pulse plate.
The present disclosure relates to the subject matter contained in Japanese patent application No. 2000-246762 (filed on Aug. 16, 2001), which is expressly incorporated herein by reference in its entirety.